Add dependency on dm-control

[azeey]

🦟 Bug fix

Summary

This allows us to do pip install sdformat-mjcf and have dm-control automatically installed.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #112 (a9de563) into main (cbafb27) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #112   +/-   ##
=======================================
  Coverage   95.30%   95.30%           
=======================================
  Files          24       24           
  Lines        1171     1171           
=======================================
  Hits         1116     1116           
  Misses         55       55           

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